The conventional water heater includes a tank to contain water to be heated and an outer jacket or casing which is spaced from the tank. It has been the practice in the past to insulate the water heater by a layer of fiber glass which is positioned in the space between the tank and the outer jacket.
More recently, water heater tanks have been insulated through use of a foamable resin, such as polyurethane. The resin is introduced in the liquid state into the space between the tank and jacket and the resin expands to fill the space and provide a semirigid foam resin insulating layer.
As the heat conductivity of the foam resin, such as polyurethane foam, is lower than that of fiber glass, the thickness of the insulation can be reduced to obtain the same insulating characteristics, as opposed to a layer of fiber glass. This results in a reduced overall size for a water heater of given capacity, thereby resulting in substantial material savings, as well as shipping and handling savings.
In the production of water heaters, certain components are installed within openings in the tank during the manufacture of the water heater, such as the thermostat, drain valve, and electric heating element, if the water heater is of an electric type. These components are generally threaded to spuds that are welded to the outer surface of the tank wall bordering openings in the tank wall, and the outer jacket of the water heater has openings through which these components extend to the exterior. With components of this type, the resin when introduced into the space between the tank and jacket, will foam around the components and bond to the components. However, the space or gap between the components and the openings in the jacket must be sealed to prevent the resin from leaking through the gap to the exterior.
Other components for the water heater, such as nipples which are connected for the water inlet and outlet pipes and the pressure relief valve, are normally installed by the plumber during the on-site installation of the water heater and thus access holes must be provided in the foam resin layer through which these components can be attached to the tank.
In one manner of providing the foam resin insulation, an annular bag is positioned in the space between the tank and jacket and serves as a compartment to receive the liquid resin. To provide access openings through the foamed resin layer, the inner and outer surfaces of the bag are pinched or heat sealed together to prevent the resin from expanding into the heat sealed areas. However, this method of providing the access openings develops openings which are of substantially different size than the components which are subsequently to be attached to the tank with the result that there are gaps in the insulation layer which reduces the overall efficiency of the insulation.